1. Field of the Invention
The present invention relates to a device for controlling the quantity of light to be used in an apparatus, such as a video camera, a still video camera, or a copying machine.
2. Description of the Related Art
Hitherto, multimedia tools for handling not only voice and alphabetic information but also image information data have been widely used. Among these multimedia tools, video cameras and digital cameras are generally used for recording the image information. Recently, by using a portable terminal, such as a mobile phone or a handheld computer, having a small integrated camera as an image-capture device, image data can be transmitted through a telephone line immediately after image capture.
Camera units of these image-capture devices are generally configured with a single focal lens unit or a zoom lens unit including lenses in a common axial system of a size suitable for each image-capture element.
FIG. 19 shows a typical known digital camera. The known digital camera includes a camera body 101, an optical part 102, an electronic flash unit 103, a release button 104, and a liquid crystal display (LCD) 105 for confirming data. The camera body 101 includes a viewfinder, an LCD for confirming recording, and the like, at the back thereof.
The optical part 102 includes a lens barrel, lenses, an image-capture element, and a diaphragm unit (light-quantity controlling unit). Incident rays from an object are led to the image-capture element through the lenses and the diaphragm unit. By an electrical circuit which is not shown, a proper diaphragm stop number and a shutter speed are determined, whereby the most appropriate exposure is performed.
In order to perform the most suitable exposure, the diaphragm stop number must be controlled in accordance with the brightness of the object. For this purpose, most video cameras generally have iris galvanometers as diaphragm units. The basic configuration of the iris galvanometer is described with reference to FIGS. 20A, 20B, and 20C.
FIGS. 20A to 20C are schematic sectional views of a known iris galvanometer. FIG. 20A is a front view, FIG. 20B is a side view, and FIG. 20C is a rear view of the known iris galvanometer.
The iris galvanometer shown in FIGS. 20A to 20C includes a casing 201, a yoke 202 formed substantially in a U-shape and made of a magnetic material, and windings 203 having conductive wires around the yoke 202, the windings 203 being connected to an electrical circuit (not shown). The iris galvanometer also includes a rotor 204 having a permanent magnet 205 and is disposed rotatably between the ends of the yoke 202. The rotor 204 is provided with two protrusions 206 and 207 at the ends of arms thereof.
The iris galvanometer includes movable blades 208 and 209 having holes 210 and 211, respectively, the blades 208 and 209 mating with the protrusions 206 and 207 at the holes 210 and 211, respectively. The blades 208 and 209 slidingly move along directions parallel to each other in the casing 201.
With reference to FIGS. 21A to 21G, the operation of the iris galvanometer, in which the size of an aperture varies, is described below.
When electric current is applied to the windings 203, the rotor 204 is rotated by a magnetic circuit in response to the current value, whereby the relative position of the movable blades 208 and 209 varies. By the movement of the blades 208 and 209, the size of an aperture 212 (the shaded portion) defined by edges of the movable blades 208 and 209 is determined, the size of the aperture 212 corresponding to each diaphragm stop number.
FIG. 21A shows the aperture 212 having a full aperture value of F2.5; FIG. 21B shows the aperture 212 having a size corresponding to F4.0; FIG. 21C shows the aperture 212 having a size corresponding to F5.6; FIG. 21D shows the aperture 212 having a size corresponding to F8.0; FIG. 21E shows the aperture 212 having a size corresponding to F11.0; FIG. 21F shows the aperture 212 having a size corresponding to F16.0; and FIG. 21G shows the aperture 212 completely closed.
As shown in these drawings, the diaphragm stop number is determined according to the rotational orientation of the rotor 204. Each edge of the movable blades 208 and 209 defining the aperture 212 is formed so that the diaphragm stop number varies continuously.
Due to the recent technological advances, components and elements used in information terminal devices have been remarkably reduced in size. In particular, charge coupled devices (CCD) as image-capture elements have been significantly miniaturized. Therefore, it is particularly important to miniaturize lenses, diaphragm units associated therewith, and the like. Because the focal distance of a lens is reduced in accordance with the reduction in the size of image-capture elements, the full aperture of the lens must be reduced when designing a lens having the same specifications. Accordingly, the aperture of a diaphragm must be further reduced, thereby causing a problem in the configuration of a known iris galvanometer.
The problem of the known iris galvanometer is that a slight play exists in the mating parts of the holes 210 and 211 provided in the movable blades 208 and 209 with the associated protrusions 206 and 207 of the rotor 204 because it is difficult to completely eliminate gaps therefrom. A play of approximately 0.1 mm is generally produced in a normal production of the known iris galvanometers in which the movable blades 208 and 209 must move smoothly. The movable blades 208 and 209 do not follow the rotational movement of the rotor 204 in the range of the play of approximately 0.1 mm.
In the past, the lens was large and had a full aperture ranging from 6 to 8 mm in diameter because image-capture elements were large. Therefore, the play of 0.1 mm was a relatively small value.
Recently, image-capture elements have become small, thereby reducing the full aperture. Known iris galvanometers generally have a full aperture of not less than 4.0 mm in diameter.
FIG. 22 is a table showing the relationship between the F-number of a lens having a full aperture of 5.24 mm in diameter and an aperture area S of 21.56 mm2, and the variation in the aperture area S when the play is 0.1 mm. The amount of variation (%) in the aperture area S is considered by dividing the play of 0.1 mm into two values with respect to the center value thereof, that is xc2x10.05 mm, the amount of variation becoming greater as the diameter of the aperture becomes smaller. The variation in exposure value (EV-value) in relation to the amount of variation (%) is also shown in the table.
The shape of the aperture is determined according to the shape of the edges of the movable blades defining the aperture. Therefore, the aperture is not always formed as a circle between the full-aperture state and the completely-closed state. However, the amount of variation in the aperture area due to the play is computed by dividing the play into two values by conveniently considering the shape of the aperture as always being a circle.
As shown in FIG. 22, when the full aperture is large, the play of 0.1 mm does not significantly affect the diaphragm stop number. The variation in the EV-value is a maximum of 0.25 when the F-number is 11, and a maximum of 0.37 when the F-number is 16, which is not a problem in practical use.
As the aperture is closed, the image quality of a lens is reduced due to the effect of diffraction. Therefore, in a general lens unit, the mechanical minimum diaphragm stop number is set in a range of F8 to F11. Below this, the minimum diaphragm stop number is obtained optically by reducing the quantity of light by using a neutral density (ND) filter or the like. In this case, the aperture size can be reduced slightly more because the mechanical accuracy in the minimum diaphragm stop number must be ensured only down to the range of F8 to F11. However, such a method using a ND filter or the like for reducing the quantity of light has a disadvantage in that a desired image-capture effect cannot be obtained because the depth of field does not vary by actuating a diaphragm. The method is not optimal from the photographer""s point of view.
When the full aperture is reduced due to the miniaturization of image-capture elements, the play of 0.1 mm strongly affects the variation in the aperture area. In FIG. 23, for a full aperture of 2 mm in diameter, the relationship between the F-number and the aperture area S and the variation in the aperture area as a percentage and in the EV-value are shown when the play is 0.1 mm. The amount of variation (%) in the aperture area S is considered by dividing the play of 0.1 mm into two values with respect to the center value thereof, that is xc2x10.05 mm, the amount of variation becoming greater as the diameter of the aperture becomes smaller. The aperture is not always formed as a circle between the full-aperture state and the completely-closed state, the shape of the aperture being determined by the shape of the edges of the movable blades defining the aperture. However, the amount of variation due to the play is computed by dividing the play into two values by conveniently considering the shape of the aperture as always being a circle.
As shown in FIG. 23, when the full aperture is reduced, the play of 0.1 mm strongly affects the diaphragm stop number. The variation in the EV-value is a maximum of 0.72 when the F-number is 11, and a maximum of 1.07 when the F-number is 16, thereby causing a problem in the exposure accuracy.
When an EV-value is set to not higher than 0.3 so as not to cause the problem in the exposure accuracy, only the F-number of 5.6 or lower can be applied, whereby a problem is caused in that the device cannot be applied to a high-brightness object.
In order to overcome the above-described problems, a diaphragm mechanism is known in which a rotatable blade having a plurality of apertures rotates and changes the size of aperture in steps (a turret-type diaphragm). However, it is difficult to reduce the size of a diaphragm mechanism of this type, and the structure thereof is complex because a particular driving mechanism is required when the diaphragm mechanism is used as a mechanical shutter.
Accordingly, a primary object of the present invention is to provide a light-quantity controlling device and an apparatus using the same, which overcome the above-described problems of known devices and apparatuses.
To this end, in an aspect of the invention, a light-quantity controlling device comprises a driving source; a first light-quantity controlling member driven by the driving source, and having a first elongated opening extending in a direction of movement of the first light-quantity controlling member; a second light-quantity controlling member driven by the driving source in a direction substantially perpendicular to the direction of movement of the first light-quantity controlling member, and having a second elongated opening extending in the direction of movement of the second light-quantity controlling member; and a supporting member configured to support the first and second light-quantity controlling members, and having an opening therein. The first and second elongated openings intersect each other at the opening provided in the supporting member when the first and second light-quantity controlling members are driven by the driving source.
The quantity of light can be controlled by the two light-quantity controlling members, supported by the supporting member having an opening, and being driven in directions substantially perpendicular to each other so that the two elongated openings intersect each other at the opening provided in the supporting member.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.